Discussion on “limitations in direct-current machine design”

Fourteen years ago or so, when all generators were small and about the time when Mr. Parshall was at work upon the 1 200 kw. machines for the World's Fair, he stated as a law what Mr. Senstius has just put in excellent form; namely, that the amperes per pole in a direct-current generator were a limited quantity. While I agree with the general method by which Mr. Senstius arrives at his limitations, I do not agree with the actual values of the limitations which he reaches. For instance, his value of 1 175 kw. for a 125-volt machine is too high; 1800 kw., for a 300-volt machine, seems about right, and 1 450 kw. for a 600-volt machine is altogether too low. I should like to ask Mr. Senstius, if he is free to speak upon the subject, how he harmonizes his limit of 1 800 kw. at 300 volts with the existence and good operation of a certain 3 500-kw., 325-volt direct-current generator in Cincinnati. It would seem that the conclusions which he reaches in his paper are not confirmed by that machine. The fact that there is a limiting size for direct-current machines, particularly in the lower voltages, ought to be better known than it is. Manufacturers are constantly receiving inquiries for generators of these lower voltages and several times larger than it is possible to construct.